Using Dual SIM with two nano-SIM cards - Apple Support
Amazon.com: Iphone Dual Sim
Amazon.com: Vodafone Spain Prepaid SIM Card 25 GB in Spain and 7 GB in the Rest of Europe, UK | 300 Min. to the US and to 55 Other Countries | Activation
Amazon.com: (10 Pack) New Nano Sim Card Adapter and Micro Sim Adapter and Nano to Micro Adapter with Sim Eject Pin Needle - (10 Pack) Black : Cell Phones & Accessories